Optical, magnetic and magneto-optic media are primary sources of high performance storage technology which enables high storage capacity coupled with a reasonable price per megabyte of storage. Use of optical media has become widespread in audio, video, and computer data applications in such formats as compact disk (CD), digital versatile disk (DVD) including multi-layer structures like DVD-5, DVD-9, and multi-sided formats such as DVD-10, and DVD-18, magneto-optical disk (MO), and other write-once and rewritable formats such as CD-R, CD-RW, DVD-R, DVD-RW, DVD+RW, DVD-RAM. In these and other formats, data are encoded onto a substrate into a digital data series. In pre-recorded media, such as CD, the data are typically pits and grooves formed on the surface of a plastic substrate through a method such as injection molding, stamping or the like.
In recordable and rewritable media, the data are encoded by laser, which illuminates an active data layer that undergoes a phase change, thus producing a series of highly-reflecting or non-reflective regions making up the data stream. In these formats, a laser beam first travels through a plastic substrate before reaching the data layer. At the data layer, the beam is either reflected or not, in accordance with the endcoded data. The laser light then travels back through the plastic and into an optical detector system where the data are interpreted.
It is well known in the art that, due to the sensitivity of the optical readout system, the amount of absorption of the light by the media should be minimized. Consequently, the plastic in the optical media is a colorless, transparent material having good birefringence properties, such as polycarbonate. Although media formats have been introduced which read data from the top-side of a substrate, the vast majority of playback systems are only compatible with media requiring the laser to travel through the substrate twice. Hence, the transparency to the laser is a requirement and colorless materials are typically used to maximize transparency at the laser wavelength.
The widespread use of colorless, transparent materials makes product differentiation difficult, except by costly printing methods on the top surface of the optical media. Furthermore, in the cases where printed decorations cover one entire surface of a disk, the covered surface is unusable for data storage.
What is needed in the art are colored plastic compositions for use as optical media.